1. Field of the Invention
The present invention relates to an agglomerate of whiskers or short fibers per se fibers usable for fiber-reinforcing various materials such as plastics, rubbers, coatings, metals and ceramics. More particularly, this invention is concerned with pelletized or granulated agglomerates of whiskers or fine short fibers having a diameter of 0.1-10 .mu.m and a length of 5-200 .mu.m.
2. Description of the Prior Art
Various methods have been known for fiber-reinforcement of a variety of molded and formed articles. Relatively large-sized articles are reinforced by the "macro-reinforcement" method. For example, woven cloths of fibers or strands or bundles of fibers having a length in the order of 50 mm are placed in the articles for reinforcement. Alternatively, preforms made from reinforcing fibers may be placed within the molds and the molding materials are subsequently injected therein to form fiber reinforced articles.
In contrast, small sized articles are generally reinforced by the "micro-reinforcement" method wherein reinforcing fibers fibers are kneaded with and dispersed in the molding material prior to molding. Short glass fibers or whiskers have been used for this purpose. Whiskers may be defined as monocrystalline or polycrystalline fibers having a cross-sectional area less than 8.times.10.sup.-5 square inches (0.2 mm in diameter) and a length greater than 10 times of the diameter.
When kneaded into the molding materials, the whiskers or glass fibers must be uniformly dispersed throughout the mass of the molding materials. Otherwise, there would be fiber rich and thin portions in the molded articles causing irregular reinforcement. Therefore, it has been the practice to use whiskers and glass fibers in the form of powders in which individual fibers are well segregated and disintegrated from each other.
The problem with such well separated whisker powders is that they are difficult to handle for storage, transportation and mixing, because they are bulky and tend to readily fly up in the air. This is particularly serious with whiskers or short glass fibers having a diameter of 0.1-10 .mu.m and a length of 5-200 .mu.m, because the bulk density thereof is in the order of 0.1 kg/liter.
In order to offset these handling problems, there has been proposed in the art to provisionally solidify the whisker powders by a binding agent. However, the binder tends to preclude individual fibers from being readily separated and uniformly dispersed when blended into the molding materials. In addition, the choice of the binding agent is limited in order to provide miscibility of the binder with the molding material.